1. Field of the Invention
The present invention relates to a valve system suited for use with light-weight small OHV-type four-cycle internal combustion engines, and more particularly, to a valve system suited for use with horizontally-opposed and V-type internal combustion engines for vehicles, ships, aircraft, stationary use, etc.
2. Description of the Background Art
OHV-type (overhead valve) four-cycle internal combustion engines have been widely used for vehicles, ships, airplanes, and stationary aircraft because of their excellent thermal efficiency, low emission of HC and other harmful emission components, low exhaust noise, and excellent drivability in a wide range of operations (See, for example, Japanese Patent Laid-open No. 2000-110516).
However, these types of internal combustion engines have several problems. For example, the valve camshafts are often heavy. The valve mechanisms operating in connection with the valve camshafts are disposed collectively at cylinder heads, e.g., at cylinder head portions of the engine. This leads to heavy cylinder head portions and increased engine proportions. This undesirable increase in size can be even greater, particularly when the number of intake and exhaust valves is increased to satisfy a requirement for increased engine output.
The aforementioned publication describes an exemplary application of an OHV-type valve mechanism for a horizontally-opposed, four-cycle internal combustion engine. However, in the example described in Japanese Patent Laid-open No. 2000-110516, valve camshafts and valve systems are positioned in head portions located at left and right extreme ends farthest from a crankshaft. Accordingly, the left and right head portions are undesirably large in size and weight.
The present invention overcomes the shortcomings associated with the background art and achieves other advantages not realized by the background art.
An object of the present invention is to provide a novel valve system for OHV-type four-cycle internal combustion engines wherein large-weight valve camshafts are disposed as near to the crankshaft as possible. Accordingly, reductions in the size and weight of the head portions of the internal combustion engine can be achieved with the novel valve system of the present invention.
These and other objects are accomplished by a valve system for an OHV four-cylinder internal combustion engine, the engine including a pair of cylinder banks disposed symmetrically on opposite sides of an imaginary line orthogonal to an axis line of a crankshaft, wherein each of the cylinder banks includes a crankcase portion for rotatably supporting the crankshaft, a cylinder block portion on an outside of the crankcase portion, and a cylinder head portion on the outside of the cylinder block portion, and the cylinder head portions enclose respective combustion chambers, the valve system comprising a plurality of intake and exhaust valves for opening and closing intake and exhaust ports of the combustion chambers being provided at the cylinder head portions; a plurality of valve camshafts operating in connection with the crankshaft, the valve camshafts being rotatably supported at the crankcase portions; a plurality of valve-operating members for operating the intake and exhaust valves; and a plurality of oscillating arms operating in connection with the valve camshafts being connected with the valve-operating members through pull rods disposed respectively on lateral sides of the cylinder banks.
These and other objects are further accomplished by a valve system for an internal combustion engine including at least a pair of cylinder banks and a crankshaft, wherein each of the cylinder banks includes a crankcase portion for rotatably supporting the crankshaft, a cylinder block on an outside of the crankcase portion, and a cylinder head portion on the outside of the cylinder block portion, the cylinder head portions enclosing respective combustion chambers, the valve system comprising a plurality of intake and exhaust valves for opening and closing intake and exhaust ports of the combustion chambers being provided at the cylinder head portions; a single valve camshaft operating in connection with the crankshaft, the valve camshaft being rotatably supported at the crankcase portions; a plurality of valve-operating members for operating the intake and exhaust valves; and a plurality of oscillating arms operating in connection with the valve camshaft being connected with the valve-operating members through pull rods disposed respectively on lateral sides of the cylinder banks.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.